The present invention relates generally to dynamoelectric machines and more particularly to control circuitry for such machines for energizing those machines from a direct current or rectified alternating current source.
Conventional direct current dynamoelectric machines employ brushes and segmented commutators for supplying current to rotor windings and have historically been plagued by arcing and wear problems associated with those brushes and commutators. More recently, motors for example, as disclosed in the abovementioned U.S. Application Ser. No. 482,409 which subsequently issued as U.S. Pat. No. 4,005,347 have been devised for direct current energization employing permanent magnet rotors without brushes or segmented commutators and their attendant problems. Typically, such brushless direct current motors may employ optical or magnetic sensing arrangements to determine the rotor position and therefore also the control required for energizing their stator supported armature windings. Additional motor leads are typically required for such position sensors and the added cost in providing such position sensors is not insignificant. The afore-mentioned contemporaneously filed application Ser. No. 729,761 provides inter alia at least one scheme for eliminating such position sensors by deriving a signal indicative of rotor speed from a determination of the current drawn through the stator windings, e.g., total line current.